1. Field of the Invention
The present invention relates to a projection exposure apparatus and method, and, more particularly, to an exposure apparatus (being a semiconductor producing apparatus) and method for precisely aligning a plate, such as a mask or reticle, and a substrate to be exposed, such as a semiconductor wafer or the like.
2. Description of the Related Art
Finer and more highly integrated semiconductor integrated circuits, large-scale integrated circuits, and the like have led to the production of more capable semiconductor exposure apparatuses that provide greater precision. There has particularly been a demand for a technique for superimposing a plate and a substrate on the order of a few tens of nanometers during alignment.
Steppers and step-and-scan apparatuses are known as such exposure apparatuses used in the production of semiconductors. They successively transfer a pattern formed on a plurality of locations of a plate (such as a reticle) onto a substrate (such as a semiconductor wafer), while the substrate is being moved in steps. Those which perform the transfer in one operation are called steppers, while those which perform the transfer while scanning the stage are called step-and-scan apparatuses. These two types of apparatuses differ in the manner of operation during exposure, but their basic operations are the same in that transfer is performed in a step-and-repeat fashion. In addition, these two types do not essentially differ in that the position of the entire region of the substrate (global) is previously determined.
In recent years, thermal expansion of the plate (reticle), during alignment of the plate and the substrate by means of a semiconductor exposure apparatus, can no longer be ignored. This problem of thermal expansion can be overcome by making corrections as a result of obtaining the thermal expansion amount from the thermal absorption rate and the exposure amount of the plate. The corrections, however, are strictly based on calculations, producing a large error from the actual expansion amount. The heat absorbed by the plate is dissipated by radiation and convection into the air, which cannot be easily and properly described by a single formula. However, the expansion amount of the plate can only be calculated from an accurate estimation of the heat absorbed by the plate and the heat dissipated from the plate.